Ultrasonic flowmeter using windowing of received signals

ABSTRACT

A method of ultrasound flow metering includes applying a first and second pulse train to an ultrasound transducer pair (T 1 , T 2 ) positioned for coupling ultrasonic waves therebetween. Responsive to the first pulse train applied to T 1 , T 1  transmits an ultrasonic wave received as received ultrasonic wave (R 12 ) by T 2  after propagating through fluid in a pipe. Responsive to the second pulse train applied to T 2 , T 2  transmits an ultrasonic wave received as received ultrasonic wave by (R 21 ) T 1  after propagating through the fluid. During the pulse trains, R 12  and R 21  build up in amplitude to provide excitation portions. The pulse trains are terminated, so that R 12  and R 21  decay as a damped free oscillation. Windowing is applied to R 12  and R 21  to generate windowed portions. A signal delay between t 12  and t 21  (ΔTOF) is calculated using only windowed portions, and a fluid flow is calculated from the ΔTOF.

FIELD

Disclosed embodiments relate to ultrasonic flowmeters, and morespecifically to signal processing of ultrasound signals for fluid flowmetering.

BACKGROUND

Ultrasonic flowmeters are commonly used to determine the flow rate for avariety of fluids (e.g., liquids, gases) flowing in pipes. Knowledge ofthe flow rate of the fluid can enable other physical properties orqualities of the fluid to be determined. For example, in somecustody-transfer applications, the flow rate can be used to determinethe volume (Q) of a fluid (e.g., oil or gas) being transferred from aseller to a buyer through a pipe to determine the cost for thetransaction, where the fluid volume is equal to the flow rate multipliedby the cross-sectional area of the pipe and the time duration ofinterest.

Non-invasive clamp-on flow monitors for pipes are known, such as forwater flow metering. A non-invasive flow monitor can be clamped to theoutside of a pipe and secured thereto, using appropriate brackets andfasteners.

Invasive inline flow monitors for pipes are also known which are mountedwithin an intervening pipe section that joins to the adjacent pipesections by a flange. One type of ultrasonic flowmeter employs transittime flow metering, where one or more pairs of ultrasonic transducersare attached to a pipe (or a spool piece attached to a pipeline), whereeach transducer pair includes a transducer located upstream with respectto the fluid flow and a transducer located downstream with respect tothe fluid flow. Each transducer, when energized, transmits an ultrasonicbeam or signal (e.g., a sound wave) along an ultrasonic path through theflowing fluid that is received by and is detected by the othertransducer of the transducer pair. The path velocity (i.e., path orchord velocity (Vp)) of the fluid averaged along an ultrasonic path canbe determined as a function of the transit time differential between thetransit time of an ultrasonic signal traveling along the ultrasonic pathfrom the downstream transducer to the upstream transducer, and thetransit time of an ultrasonic signal traveling along the ultrasonic pathfrom the upstream transducer to the downstream transducer.

There are two different measurement principles used in known transittime ultrasonic flowmeters. A first type of ultrasonic flowmeter is adirect path type that implements direct measuring crossed paths betweentransducer (sensor) pairs, where there are no reflectors needed. Theultrasonic transmitter and receiver for the direct-path type ultrasonicflowmeter are located in a linear configuration within the fluid flowinginside the meter pipe. A second type of ultrasonic flowmeter is areflective path type that implements indirect measuring paths generallyusing at least one ultrasonic reflector mounted on the meter pipe innerwall opposite to the transducer pair to reflect the ultrasonicmeasurement signal received from the ultrasonic transmitter to theultrasonic receiver, where the transducer pair is located at the sameside of the meter pipe wall.

In operation, a pulse train excitation is generally used to excite onetransducer of the transducer pair. A conventional way to process thereceived ultrasonic signal resulting from the pulse train excitation isto compute the zero crossings of the received signal from which thedifference in transit time (or delta time of flight, ΔTOF) between theupstream and downstream paths is calculated, which is used to computethe fluid flow.

SUMMARY

This Summary briefly indicates the nature and substance of thisDisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims.

Disclosed embodiments recognize for fluid flow monitoring there is aneed for accurate processing of received ultrasonic signals responsiveto applied pulse train excitation. In disclosed methods of ultrasoundflow metering and related processor integrated circuits (ICs) andultrasonic flowmeters therefrom a pulse train including multiple (e.g.,20) pulses are transmitted (such as by an microcontroller unit (MCU)) toa transmit transducer that transmits an ultrasound signal, which ispicked up by a receive transducer after passing through a fluid pathreferred to as a channel.

During the excitation period, the received signal builds up inamplitude, and given sufficient time builds up to a nominal steady stateamplitude oscillating at the excitation frequency. Once the pulseexcitations are stopped, the received signal at the receiving transducerdecays at the resonant frequency of the entire system which isrecognized to be temperature dependent, and to also be dependent onother variables including for fluid mixtures the concentration ofcomponent(s), and impurity level(s). Accordingly, to calculate thedifference in propagation time between the downstream and upstreamsignals (or Δ time of flight (TOF)) defined as the time between t₁₂ andt₂₁, respectively, which enables a fluid flow to be calculated, whereint₁₂ is a time for said ultrasonic wave to propagate from the firsttransducer (T₁) to the second transducer (T₂) and t₂₁ is time for theultrasonic wave to propagate from T₂ to T₁, it is recognized ΔTOFmeasurement accuracy can be improved by applying a window function forwindowing the respective received ultrasonic waves (R₁₂) and (R₂₁) togenerate windowed portions. In one embodiment the windowing of R₁₂ andR₂₁ passes only the excitation portion of R₁₂ and R₂₁, so thatcomputation is performed only on the excitation portion of the receivedsignals, and the decaying region (tail) is filtered out and is thusdiscarded.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1 is a flow chart that shows steps in an example method ofultrasound flow metering using windowing of the received ultrasonicsignals, according to an example embodiment.

FIG. 2 depicts an example ultrasonic flowmeter shown installed betweenpipeline sections, according to an example embodiment.

FIG. 3 shows an example monolithic mixed signal processor ICimplementing a disclosed method of ultrasound flow metering usingwindowing of the received ultrasonic signals, according to an exampleembodiment.

FIG. 4A depicts an example ultrasonic flowmeter including the MCU shownin FIG. 3 and a pipe section having transducers and reflectors withinthe pipe section with an example transmitted pulse train (TX) and thereceived signal (RX) after amplification and analog-to-digital (ADC)conversion shown above.

FIG. 4B show an expanded view of RX shown in FIG. 4A.

FIG. 4C shows an evaluation of the peak frequency (in MHz) of the RXsignal at zero fluid flow, and across a range of temperatures from about5° C. to 85° C.

FIG. 5A shows an excitation portion after the windowing that filteredout entire tail portion of the signal shown in FIG. 4B.

FIG. 5B shows an example linear tapering window shown as a trapezoidalwindow having a linear ramp.

FIG. 6A and FIG. 6B show the ΔTOF at zero flow for 2 different waterflow meters computed using both disclosed windowing (only the excitationportion) and with no-windowing (excitation portion and the tail portion)of the received signal.

DETAILED DESCRIPTION

Example embodiments are described with reference to the drawings,wherein like reference numerals are used to designate similar orequivalent elements. Illustrated ordering of acts or events should notbe considered as limiting, as some acts or events may occur in differentorder and/or concurrently with other acts or events. Furthermore, someillustrated acts or events may not be required to implement amethodology in accordance with this disclosure.

Also, the terms “coupled to” or “couples with” (and the like) as usedherein without further qualification are intended to describe either anindirect or direct electrical connection. Thus, if a first device“couples” to a second device, that connection can be through a directelectrical connection where there are only parasitics in the pathway, orthrough an indirect electrical connection via intervening itemsincluding other devices and connections. For indirect coupling, theintervening item generally does not modify the information of a signalbut may adjust its current level, voltage level, and/or power level.

FIG. 1 is a flow chart that shows steps in an example method 100 ofultrasound flow metering using windowing of the received ultrasonicsignals, and calculating a signal delay using the windowed receivedultrasonic signals, according to an example embodiment. Step 101comprises applying a plurality of electronic pulses (pulse train) to anultrasound transducer (transducer) pair including a first transducer(T₁) and at least a second transducer (T₂) positioned for couplingultrasonic waves between T₁ and T₂. The transducers along with one ormore optional ultrasonic reflectors can be within a pipe section toprovide an inline flowmeter. The propagation path can be reflective(through the inner wall of the pipe reflecting or through addedreflectors on the inner pipe wall) or direct (straight or diagonal).Alternatively, the transducers may be clamped on in a non-intrusiveclamp-on arrangement.

The excitation frequency selected can be at or near the resonancefrequency of the transducers. As used herein, near the resonantfrequency of the transducers means within 5% of the resonant frequency.The result of selecting an excitation frequency at or near the resonancefrequency of the transducers is recognized to improve the signal tonoise ratio (SNR) of the received signals and to improve the performance(i.e. accuracy) of the TOF computations.

Step 102 comprises responsive to a first pulse train applied to T₁, T₁transmitting an ultrasonic wave that is received as a receivedultrasonic wave by T₂ (received signal R₁₂) after propagating through afluid in the pipe section. Step 103 comprises responsive to a secondpulse train applied to T₂, T₂ transmitting an ultrasonic wave that isreceived as a received ultrasonic wave by T₁ (received signal R₂₁) afterpropagating through the fluid. The first and second pulse trains aregenerally matching (the same) pulse trains.

Step 104 comprises during the pulse trains, R₁₂ and R₂₁ building up inamplitude to provide an excitation portion. Step 105 comprisesterminating the pulse trains, wherein after the terminating R₁₂ and R₂₁decay as a damped free oscillation which oscillates at a resonantfrequency of the entire system, which as described above is recognizedto be sensitive to temperature. The damped free oscillations can providea tail portion (see FIG. 4B described below).

Step 106 comprises windowing R₁₂ and R₂₁ to generate windowed portions.Disclosed windowing is performed in the time domain. As known in signalprocessing, a window function provides windowing (also known as anapodization function or tapering function) by applying a mathematicalfunction that is zero-valued outside of some selected interval to asignal of interest. For instance, a function that is constant inside theinterval and zero elsewhere is referred to as a rectangular window,which describes the shape of its graphical representation. When anotherfunction or waveform/data-sequence is multiplied by a window function,the product is also zero-valued outside the interval, with the remainingsignal being the part where they overlap. In one particular embodimentthe windowing selectively removes the tail portion to only pass theexcitation portion. The windowing can also remove unwanted portions ofthe received signal that are not part of the buildup and tail portionsand to only select specific portions of the received signal waveforms.

Step 107 comprises calculating a signal delay between t₁₂ and t₂₁(ΔTOF)) using only the windowed portions. As noted above t₁₂ is a timefor the ultrasonic wave to propagate from T₁ to T₂ and t₂₁ is time forthe ultrasonic wave to propagate from T₂ to T₁. ΔTOF=t₁₂−t₂₁, assumingt₁₂ is the downstream direction and t₂₁ is the upstream direction.

t ₁₂ =L/(c+ν); t ₂₁ =L/(c−ν), ΔTOF=t ₁₂ −t ₂₁

Where txy is the TOF from x to y, L is the distance between the transmitand receive transducers (T₁, T₂), c is the velocity of theultrasonic/sound wave, and a is the velocity of measurand. Step 108comprises calculating a flow of the fluid from the calculated ΔTOF. Twoexample calculation approaches are described below for determining ΔTOFshown below as ΔT:

Example Approach 1:

with knowing c as a function of temperature and the temperature ofmeasurand ΔT can be determined with the equation below:

$0 = {v^{2} + {\frac{2L}{\Delta \; T}v} - c^{2}}$

Example approach 2: No temperature measurement needed, only thecalculation of the absolute time of flights t₁₂ and t₂₁:

ν=L/2×(1/t ₁₂−1/t ₂₁)=L/2×(t ₂₁ −t ₁₂)/(t ₂₁ t ₁₂)=L/2×(ΔT)/(t ₂₁ t ₁₂)

The Equations above are for flowmeters where the ultrasound wave travelsin a straight line between the respective transducers. For the inlineultrasonic flowmeter 200 shown in FIG. 2 described below that operateswith a ultrasound wave that does not travel in a straight line betweenthe two transducers T₁ and T₂, one should replace L with L cos(Θ), whereL is the distance travelled by the ultrasound wave between T₁ and T₂ andΘ is the angle between the path taken by the ultrasound wave and theline between T₁ and T₂.

FIG. 2 depicts an example inline ultrasonic flowmeter 200 showninstalled between pipeline sections 230 a and 230 b includingtransducers 201 and 203 positioned on one side of the inner part of themeter pipe wall 205 a along with an optional ultrasonic reflector 212,according to an example embodiment. The ultrasonic flowmeter 200includes a meter body 205 including the meter pipe wall 205 a.Connection flanges 208 are shown on each end of the ultrasonic flowmeter200 for bolting the ultrasonic flowmeter 200 to the pipeline sections230 a and 230 b.

Transducer 201 and 203 on first portion 205 ₁ of the pipe meter wall 205a together provide a first transducer pair. The ultrasonic reflector 212is generally positioned on the inner side of the meter pipe wall 205 aand functions to increase the efficiency (ultrasonic signal intensity)of the reflective path for the transducer pair. The reflector 212 isgenerally in the conventional form of a metal plate.

The transducers 201, 203 have assembly angles and emission patterns forproviding the desired measurement path shown as a V pattern. In anotherarrangement two spaced apart reflectors on the second portion 205 ₂allows a rectangular shaped measurement path (see FIG. 4A describedbelow). The flow electronics module 220 is shown including a processor221 and an associated memory 222 (e.g., static random access memory(SRAM)) that stores a disclosed flow measurement algorithm 223 that useswindowing, and a transceiver 225, which collectively provides anultrasonic computer-based electronic flow measuring system that iscoupled to the transducers 201, 203 for causing the one transducer totransmit ultrasonic signals and for analyzing received sensing signalsgenerated by the other transducer to determine a volume flow of a fluidflowing through the ultrasonic flowmeter 200. As used herein, atransducer can include a separate transmitter and receiver. Other flowelectronics module electronics, such as signal amplifiers, filters, ananalog-to-digital converter (ADC, in the receive circuitry) anddigital-to-analog converter (DAC, in the transmit circuitry) aregenerally part of flow electronics module 220, but are not shown toprovide simplicity.

Ultrasonic flowmeter 200 can measure the flow velocity of the fluidflowing therethrough using the transit times of ultrasonic pulses, andflow electronics module 220 can calculate the flow rate at measurementconditions therefrom. Used is the fact that ultrasonic pulses travelfaster in the direction with the flow than in the direction against theflow.

During operation, each of the transducers 201, 203 generally function asboth an emitter (transmitter) and a receiver (at different times).Measurements are taken alternatively in both directions, so that after atransit time has been measured, an emitter becomes the receiver and viceversa. In this way, the impact of the speed of sound which depends onthe fluid type, pressure and temperature is reduced.

FIG. 3 is a block diagram depiction of an example mixed signal processorIC shown as MCU 300 formed in and on a semiconductor surface 305 a of asubstrate 305 including a non-volatile memory 372 (e.g., flash memory)storing a disclosed flow measurement algorithm 223 that implementsdisclosed windowing of received ultrasonic signals, according to anexample embodiment. On-chip flash memory is most often the source forall the instructions for the central processing unit (CPU or processor)375. The processor IC 300 can comprise a microprocessor, digital signalprocessor (DSP) or the MCU shown. Although flow measurement algorithm223 is shown as stored software in non-volatile memory 372 implementedby CPU 375, circuitry (i.e., hardware) on MCU 300 can be used in wholeor in part to implement a disclosed flow measurement algorithm.

Although not shown, the processor IC 300 generally includes otherintegrated circuit modules, for example, a Universal Serial Bus (USB)controller and a transceiver. Processor IC 300 is shown also includingADC's 343 a, 343 b, PWM driver 355, volatile data memory 373, digitalI/O (interface) 374, and clock (or timer) 376. Processor IC 300 is alsoshown including a digital data bus 378 and an address bus 379. There aregeneral purpose input/output pins (GPIOs) 351, 352 which are coupled tothe data bus 378 and to the address bus 379. The GPIOs 351, 352 areshown in FIG. 3 coupled to transducers T₁ and T₂, respectively, where T₁and T₂ can be transducers 201 and 203 shown in the inline ultrasonicflowmeter 200 of FIG. 2.

FIG. 4A depicts an example ultrasonic flowmeter shown as 400 includingthe MCU 300 shown in FIG. 3 and a pipe section 410 having transducers T₁and T₂ and reflectors R1 and R2 within with an example transmitted pulsetrain (TX) and the received signal (RX) after amplification and ADCconversion described above. GPIO pins 351, 352 are in the coupling pathbetween the MCU 300 and T₁ and T₂. When transducers T₁ and T₂ areexcited by the pulse train TX at a frequency near the resonant frequencyof T₁ and T₂ (e.g., 1 MHz), RX is received at the receiving transducer.RX is shown having an excitation portion which has a buildup inamplitude with time from the pulse train and the later in time tailportion which has an amplitude decaying with time.

Distinguishing features of disclosed embodiments include capture of theentire received waveform and correlating the upstream and downstreamreceived ultrasound signals accurately to compute the ΔTOF. To obtainthe accurate ΔTOF, the receive signal are windowed to generate windowedportions, in one particular embodiment so that only the excitationportion is selected. Advantages include due to windowing of receivedultrasound data the ΔTOF is accurately computed and variations in ΔTOFto temperature changes are reduced because it is recognized the tailportion typically is governed by the natural frequencies of thetransducers which are different. Furthermore, the natural frequencies ofthe transducers may change with temperature of the fluid medium, thuscausing a drift in the ΔTOF if the tail portion is also included in theTOF correlation calculation. Other benefits include reducing thecomputation needed for TOF calculation, and increasing the frequency forwhich the upstream/downstream signaling can occur as there is no need towait for the tail amplitude to die down.

As used herein and by way of example and not by limitation, “hardware”can include a combination of discrete components, an integrated circuit,an application-specific integrated circuit, a field programmable gatearray, a general purpose processing or server platform, or othersuitable hardware. As used herein and by way of example and not bylimitation, “software” can include one or more objects, agents, threads,lines of code, subroutines, separate software applications, one or morelines of code or other suitable software structures operating in one ormore software applications or on one or more processors, or othersuitable software structures. In one example embodiment, software caninclude one or more lines of code or other suitable software structuresoperating in a general purpose software application, such as anoperating system, and one or more lines of code or other suitablesoftware structures operating in a specific purpose softwareapplication.

Examples

Disclosed embodiments are further illustrated by the following specificExamples, which should not be construed as limiting the scope or contentof this Disclosure in any way.

FIG. 4B show an expanded view of the RX shown in FIG. 4A. As shown inFIG. 4B, RX has two parts identified, an excitation portion which is thebuildup of the pulses from an applied pulse train having 20 pulsescorresponding to time about 5 to 23 μsec, and the later in time tailportion corresponding to time about 23 μsec to 55 μsec which iscorresponds to the decay with free oscillations of the system. The tailportion is seen to freely oscillate in a damped amplitude pattern atsystem's resonance frequency. However, as noted above, the system'sresonant frequency is dependent on the temperature of the fluid medium,and can include other dependencies such as the concentration of onecomponent in a fluid mixture in the case of fluid mixtures.

FIG. 4C shows an evaluation of the peak frequency (in MHz) of the RXsignal at zero fluid flow, and across a range of temperatures from about5° C. to 85° C. As shown in FIG. 4C the tail portion of RX hassignificantly more temperature dependence as compared to the excitationportion of the received signal. Hence using entire data (excitationportion plus the tail portion) for signal processing makes the resultsmore dependent on the temperature of channel.

To reduce the temperature dependence on the computation and theresulting impact on ΔTOF, as described above, windowing of RX is used togenerate windowed portions, such as in one particular embodiment to onlyuse the excitation region of the RXs for further processing. As notedabove, the excitation region naturally decays in amplitude over time inthe tail portion. Hence RX can be windowed by a suitable window functionto extract the excitation portion and filter out other portions, such asthe entire tail portion as shown in FIG. 5A. A rectangular (short riseand fall time) window can be used, however abrupt termination of theexcitation part can result in high frequency ringing of the resultingwindowed signal. To avoid ringing, a smoother window such as Hanning (orHann) window can be used. The Hanning window (ω(n)) is given by:

${\omega (n)} = {0.5\left( {1 - {\cos\left( \frac{2\pi \; n}{N - 1} \right)}} \right)}$

where the ends of the cosine just touch zero, so the side-lobes roll offat about 18 dB per octave. For a low complexity computation, a linearlytapering window, shown as a trapezoidal window having a linear rampwindow with a ramp slope as shown in FIG. 5B can be used to smooth outthe edges instead of a sharp (fast rise time) rectangular window.

FIG. 6A and FIG. 6B show the ΔTOF result at zero flow for 2 differentwater flow meters computed using both disclosed windowing (resulting inthe windowed RX having only the excitation portion) and knownnon-windowed (RX has both the excitation portion and the tail portion)of RX. It can be clearly seen from both FIGS. 6A and 6B that the resultsfrom the windowed RX (excitation portion only) on both the flowmetersfollow the temperature profile which as described above improves theaccuracy of the TOF calculation. This behavior is not the case for theknown non-windowed results (RX having the excitation portion and tailportion). Although it appears the results using non-windowed RX isbetter in flowmeter as shown in FIG. 6A, because the ΔTOF is neitherindependent nor tracking the temperature profile shown, the results arenot reliable being dependent on the channel conditions, particularly thefluid temperature.

Those skilled in the art to which this disclosure relates willappreciate that many other embodiments and variations of embodiments arepossible within the scope of the claimed invention, and furtheradditions, deletions, substitutions and modifications may be made to thedescribed embodiments without departing from the scope of thisdisclosure. For example, by applying a threshold on the RX signal andcapturing zero crossings only in the excitation region, it is possibleto compute the phase difference and ΔTOF. However the accuracy of thisarrangement may be affected by the noise floor and the signal to noiseratio (SNR).

1. A method of ultrasound flow metering, comprising: applying aplurality of electronic pulses (pulse train) including a first and asecond pulse train to an ultrasound transducer (transducer) pairincluding a first transducer (T₁) and at least a second transducer (T₂)positioned for coupling ultrasonic waves between said T₁ and said T₂;responsive to said first pulse train applied to said T₁, said T₁transmitting an ultrasonic wave that is received as a receivedultrasonic wave (R₁₂) by said T₂ after propagating through a fluid in apipe section; responsive to a second said pulse train applied to saidT₂, said T₂ transmitting an ultrasonic wave that is received as areceived ultrasonic wave (R₂₁) by said T₁ after propagating through saidfluid; wherein during said pulse trains, said R₁₂ and said R₂₁ build upin amplitude to provide an excitation portion; terminating said pulsetrains, wherein after said terminating said R₁₂ and said R₂₁ decay as adamped free oscillation; windowing said R₁₂ and said R₂₁ to generatewindowed portions; calculating a signal delay between t₁₂ and t₂₁ (Δtime of flight (TOF)) using only said windowed portions, wherein saidt₁₂ is a time for said ultrasonic wave to propagate from said T₁ to saidT₂ and said t₂₁ is a time for said ultrasonic wave to propagate fromsaid T₂ to said T₁, and calculating a flow of said fluid from said ΔTOF.2. The method of claim 1, wherein said windowing comprises using alinearly tapered window.
 3. The method of claim 1, said windowingcomprises using a Hanning window.
 4. The method of claim 1, wherein saidfluid comprises water.
 5. The method of claim 1, wherein said T₁ andsaid T₂ are spaced apart from one another along a first pipe wall of aninline pipe section.
 6. The method of claim 1, wherein said damped freeoscillation provides a tail portion, and wherein said windowingselectively removes at least a section of said tail portion.
 7. Themethod of claim 1, wherein an excitation frequency for said pulse trainis at or within 5% of a resonant frequency of said T₁ and said T₂.
 8. Amonolithic mixed signal processor IC (processor IC), comprising: asubstrate having a semiconductor surface; a processor formed on saidsemiconductor surface; a non-volatile memory storing a flow measurementalgorithm; a data bus for coupling said non-volatile memory to saidprocessor; an address bus for coupling said non-volatile memory to saidprocessor; input/output (IO) pins, coupled to said data bus and saidaddress bus for coupling to a first transducer (T₁) and to a secondtransducer (T₂); said flow measurement algorithm when said IO pins arecoupled to an ultrasound transducer (transducer) pair including said T₁and at least said T₂ positioned for coupling ultrasonic waves betweensaid T₁ and said T₂ and when implemented by said processor sequencingsaid IC for: applying a plurality of electronic pulses (pulse train)including a first and a second pulse train to said T₁ and said T₂,wherein responsive to said first pulse train applied to said T₁, said T₁transmitting an ultrasonic wave that is received as a receivedultrasonic wave (R₁₂) by said T₂ after propagating through a fluid in apipe section, and responsive to a second said pulse train applied tosaid T₂, said T₂ transmitting an ultrasonic wave that is received as areceived ultrasonic wave (R₂₁) by said T₁ after propagating through saidfluid, wherein during said pulse trains, said R₁₂ and said R₂₁ build upin amplitude to provide an excitation portion; terminating said pulsetrains, wherein after said terminating said R₁₂ and said R₂₁ decay as adamped free oscillation which are received by said IC; windowing saidR₁₂ and said R₂₁ to generate windowed portions; calculating a signaldelay between t₁₂ and t₂₁ (Δ time of flight (TOF)) using only saidwindowed portions, wherein said t₁₂ is a time for said ultrasonic waveto propagate from said T₁ to said T₂ and said t₂₁ is a time for saidultrasonic wave to propagate from said T₂ to said T₁, and calculating aflow of said fluid from said ΔTOF.
 9. The processor IC of claim 8, saidwindowing comprises using a linearly tapered window.
 10. The processorIC of claim 8, wherein said windowing comprises using a Hanning window.11. The processor IC of claim 8, wherein said damped free oscillationprovides a tail portion, and wherein said windowing selectively removesat least a section of said tail portion.
 12. The processor IC of claim8, wherein said processor IC comprises a microcontroller unit (MCU). 13.An ultrasonic flowmeter, comprising: at least ultrasonic transducers(transducers) positioned on a pipe wall including at least a firsttransducer pair including a first transducer (T₁) and at least a secondtransducer (T₂) positioned for coupling ultrasonic waves between said T₁and said T₂; a flow electronics module including a transceiver coupledto a processor having an associated memory storing a flow measurementalgorithm coupled to said transducers for: applying a plurality ofelectronic pulses (pulse train) including a first and a second pulsetrain to said T₁ and said T₂, wherein responsive to said first pulsetrain applied to said T₁, said T₁ transmitting an ultrasonic wave thatis received as a received ultrasonic wave (R₁₂) by said T₂ afterpropagating through a fluid in a pipe section, and responsive to asecond said pulse train applied to said T₂, said T₂ transmitting anultrasonic wave that is received as a received ultrasonic wave (R₂₁) bysaid T₁ after propagating through said fluid, wherein during said pulsetrains, said R₁₂ and said R₂₁ build up in amplitude to provide anexcitation portion; terminating said pulse trains, wherein after saidterminating said R₁₂ and said R₂₁ decay as a damped free oscillationwhich are received by said IC; windowing said R₁₂ and said R₂₁ togenerate windowed portions; calculating a signal delay between t₁₂ andt₂₁ (Δ time of flight (TOF)) using only said windowed portions, whereinsaid t₁₂ is a time for said ultrasonic wave to propagate from said T₁ tosaid T₂ and said t₂₁ is a time for said ultrasonic wave to propagatefrom said T₂ to said T₁, and calculating a flow of said fluid from saidΔTOF.
 14. The ultrasonic flowmeter of claim 13, wherein said T₁ and saidT₂ are spaced apart from one another along a first pipe wall of aninline pipe section.
 15. The ultrasonic flowmeter of claim 13, whereinsaid windowing comprises using a Hanning window.
 16. The ultrasonicflowmeter of claim 13, wherein said damped free oscillation provides atail portion, and wherein said windowing selectively removes at least asection of said tail portion.
 17. The ultrasonic flowmeter of claim 13,wherein said processor comprises a microcontroller unit (MCU).